This project is an extension of previous work directed toward the study of noninvasive methods to determine spatial and temporal relationships existing between tissues of clinical interest. The approach involves in vitro modelling of promising systems and the development of prototypes suitable for clinical evaluation. Recent work has focused on studies directed toward development of a versatile computerized radiographic system designed to be used both fluoroscopically and off-line to produce images which can be subtracted to show small changes in tissue occuring over long intervals of time, and combined in ways permitting tomographic display of specific slices of individual teeth. An all-electronic prototype is being fabricated which couples a specially developed extraoral x-ray source having a tiny focal spot which can be positioned under computer control on an extended target, to a miniaturized video imaging system. This design differs from earlier prototypes in that it is both similar and better suited to dental applications. This system has been simulated using images produced with components having comparable performance specifications. Results confirm that clinically meaningful subtraction images can be produced without the need for an occlusal stint to stabilize projection geometry and further that the system can be used to synthesize any desired x-ray projection from a series of related projections having known geometric properties. Other diagnostic systems are being studied which involve the predictability of a new measure of illness severity as applied within the context of a hospital intensive care environment.